Unique catalytic activities have been reported in nanoscale materials in recent years, as described by D. Astruc, et al. in Angew Chem Int Ed Engl 2005, 44, 7852. The nanoscale or size-dependent properties are often absent in bulk materials and are the basis for designing novel catalysts with multiple applications in energy storage, chemical synthesis and biomedical applications. Cerium oxide has been used extensively in catalytic converters for automobile exhaust systems, as an ultraviolet absorber and as an electrolyte for fuel cells.
Most recently, it has been found that nanosized cerium oxide (nanoceria) possesses antioxidant activity at physiological pH and their potential use in biomedical applications such as protection against radiation damage, oxidative stress and inflammation has been reported by various researchers, such as, R. W. Tarnuzzer, et al. in Nano Lett 2005, 5, 2573; J. P. Chen, et al. in Nature Nanotechnology 2006, 1, 142; J. Niu, et al in Cardiovasc Res 2007, 73, 549; M. Das, et al. in Biomaterials 2007, 28, 1918 and J. M. Perez, et al. in Small 2008, 5, 552-556.
The ability of these nanoparticles to act as an antioxidant resides in their ability to reversibly switch from Ce+3 to Ce+4 as reported by M. Das, et al. in Biomaterials 2007, 28, 1918. Furthermore, the synthesis of a biocompatible dextran-coated nanoceria (DNC) preparation and enhanced stability in aqueous solution has been recently reported in co-pending U.S. patent application Ser. No. 11/965,343 filed on Dec. 27, 2007, the content of which is incorporated herein by reference; it was also reported that the polymeric coating does not affect the autocatalytic properties of nanoceria, as hydrogen peroxide and peroxyl radicals can diffuse through the hydrophilic polymer coating and oxidize Ce+3 to Ce+4. Thus, coated nanoceria particles are used as antioxidants in biomedical applications, such as, protection against radiation damage, oxidative stress and inflammation.
In co-pending U.S. patent application Ser. No. 12/169,179, the content of which is incorporated herein by reference; it is reported that in-situ synthesized coated nanoceria particles with enhanced biocompatibility and stability in aqueous solution exhibit a pH-dependent antioxidant activity and provide a means for tailoring reversible and non-reversible antioxidant properties of coated nanoceria particles.
A journal article by Atul Asati, Santimukul Santra, Charalambos Kaittanis, Sudip Nath, J. Manuel Perez, entitled, “Oxidase Activity of Polymer-Coated Cerium Oxide Nanoparticles” published in Angew. Chem. Int. Ed. 2008, 47, 2308-2312 (DOI: 10.1002/ANIE.200805279) and was subsequently published on-line Jan. 7, 2009.
It is desirable to extend the utility of the coated nanoceria particles as a stable, effective catalyst and oxidant replacing less desirable oxidants, such as, hydrogen peroxide, that are chemically unstable and harmful to biological tissue and the environment. The present invention provides a much needed solution to problems in the prior art.